Well, to be quite honest, I have not looked at the site for the directory, in a very, very, long time.
It used to be that it was based upon the edition of the directory that one had and you would be referred to a page and to look for a specific word.
According to the website for Southwest Frequency Directory, it says:
Southwest Frequency Directory - 10th Edition
Enter your email address and click "submit" to receive updates to the Southwest Frequency Directory by email. You will also receive a password to access the Publication Updates Archive System for email updates you may have missed."
It then gives you the option to subscribe or unsubscribe.
So, there you have it. Give that a try.
Scannerstuff Publication Updates - Free Subscription